In a manufacturing line of a factory, a variety of devices is attached to a control panel. In order to generalize the attaching of the devices, a standardized attachment rail may be used. One of such rail is, for example, a DIN rail. The DIN rail is shaped to have ledges on both sides of the DIN rail in a width direction of the DIN rail, and each ledge protrudes from a center part of the DIN rail by a few millimeters and has approximately 5 millimeters of dimension in the width direction. On the other hand, a device to be attached to the DIN rail includes a housing provided with an attachment structure that attaches the housing to the DIN rail, for example, as disclosed in Patent Document 1 (JP 2013-214632 A) or Patent Document 2 (JP 2005-064114 A).
In such attachment structure of the housing, a recess is provided on the housing such that a widest portion of the rail is fit to the recess. In a state where the housing is fitted to the rail, an operable portion is operated to cause a claw as an engagement portion to protrude toward the ledge of the rail and to prevent the housing from dropping from the rail. An inner wall of the recess of the housing is in contact with side edges of the rail and limits movement of the housing in the width direction of the rail. In such state, since the claw protrudes toward and engages with the ledge of the rail, the housing can be prevented from dropping from the rail even when the housing moves in an up-down direction.
Conventional attachment structures of housings have some variations of claws engaging ledges provided on opposite sides of a rail. One of the variations is a structure including a movable claw and a fixed claw as a pair of claws which are located on an upper side and a lower side of the rail, respectively, and corresponds to ledges on opposite sides of the rail in its width direction. When such housing is attached to the rail, the fixed claw is first engaged with one of the ledges of the rail, and then the movable claw is engaged with another of the ledges of the rail. Another of the variations is a structure in which both of claws are movable. In this case, a recess of the housing is fitted to the rail first, and then an operable portion is operated to move the both claws inward of the rail in the width direction to be engaged with the respective ledges of the rail.
When one of the claws is fixed, a structure for moving the movable claw by operation of the operable portion can be made to be simple. However, since the fixed claw is used, an attachment procedure may become complicated. For example, when the housing is attached to the rail, the fixed claw is first engaged with the ledge of the rail while the housing is inclined with respect to the rail, and then the operable portion is operated while the housing is pressed against the rail. Furthermore, if the engagement of the fixed claw with the ledge is failed, the fixed claw may be broken. On the other hand, when both of the claws are movable, such breakage of the claw may not occur, but a structure for moving the claws in opposite directions may become complicated. When two operable portions are provided for the respective claws to move individually, the operator needs to operate the two operable portions separated in the up-down direction, in other words, operability of the attachment structure is not sufficient.